This application concerns star polymers and their preparation with functional acrylic arms made by group transfer polymerization (GTP) and cross-linked cores made by condensation reactions involving the functional groups on the arms.
1. Preparation of Hydrocarbon Star Polymers
Star polymers derived from unsaturated hydrocarbon monomers, such as styrene, butadiene and isoprene, have been obtained by preparing lithium-terminated "living" polymers via anionic polymerization and then coupling the "living" polymer chains by reacting them with various polyfunctional linking agents. This has usually produced hydrocarbon star polymers with relatively few (3-12) arms. Hydrocarbon star polymers with a larger number of arms (e.g., 15-56) have been obtained by sequential anionic polymerization of difunctional monomers (e.g., divinylbenzene) with monofunctional monomers (e.g., styrene) or with monomers that behave as monofunctional monomers (e.g., isoprene). Both methods of preparing hydrocarbon star polymers have been reviewed by B. J. Bauer and L. J. Fetters in Rubber Chem. and Technol. (Rubber Reviews for 1978), Vol. 51, No. 3, pp 406-436 (1978).
A. Aoki et al., U.S. Pat. No. 4,304,881 (1981), prepared styrene/butadiene "living" polymers by anionic polymerization and then coupled them by reaction with silicon tetrachloride to produce a 4-arm star polymer having a silicon core in Example 4.
H. T. Verkouw, U.S. Pat. No. 4,185,042 (1980), prepared a polybutadiene "living" polymer by anionic polymerization and then prepared a silicon-containing 3-arm by reacting the "living" polymer with gamma-glycidoxypropyltrimethoxysilane in Example 5.
R. Milkovich, U.S. Pat. No. 4,417,029 (1983), prepared a hydrocarbon star polymer having 10 arms of 2 kinds. Of the 10 arms, 5 were a diblock copolymer of polystyrene (Mn=12,300) and polyisoprene (Mn=52,450). The other 5 arms were polyisoprene (Mn=52,450). The hydrocarbon star polymer was prepared by charging sec-butyllithium, then styrene, them more sec-butyllithium, then isoprene, then divinylbenzene at a mole ratio of divinylbenzene to sec-butyllithium initiator of 5.5:1. Subsequent reaction of the "living" lithium sites in the core with carbon dioxide or ethylene oxide produced carboxylic acid or hydroxyl groups respectively in the core in Example 2.
T. E. Kiovsky, U.S. Pat. No. 4,077,893 (1978), suggested reacting lithium-terminated "living" polymers derived from diene monomers (e.g., butadiene or isoprene) with divinylbenzene to form a 4-25 arm star polymer and then reacting the (still living) star polymer with the same or a different monomer to grow further polymer chains from the core. Thus, star polymers having two kinds of arms were proposed in Col. 5, lines 40-58.
A series of Dow Chemical patents including U.S. Pat. Nos. 4,587,329; 4,599,400; 4,468,737; 4,558,120; and 4,507,466 are directed to hyper-branched non-acrylic stars such as of polyamide or polyether condensation polymers with two or more ends per branch. These are discussed in "Dendritic Macromolecules: Synthesis of Starburst Dendrimers"--Tornalia, et al. Macromolecules 19, No. 9, 2466-2468 (1986).
W. Burchard and H. Eschway, U.S. Pat. No. 3,975,339 (1976), reacted a mixture of 50% divinylbenzene and 50% ethylvinylbenzene in toluene with n-butyllithium to produce a polydivinylbenzene microgel having 270 active lithium-carbon bonds per molecule. This was subsequently reacted with styrene to produce a star polymer having 270 arms, each arm having a weight average molecular weight of 17,500 in Example 1.
H. Eschway, M. L. Hallensleben and W. Burchard, Die Makromolekulare Chemie, Vol. 173, pp 235-239 (1973), describe the anionic polymerization of divinylbenzene using butyllithium to produce soluble "living" microgels of high molecular weight. These microgels were then used to initiate polymerization of other monomers to produce star polymers. The number of arms depended on the number of active sites in the "living" microgel, which in turn depended on the mole ratio of divinylbenzene to butyllithium initiator. To avoid gellation it was necessary to work at low concentrations (e.g., 2.5% in benzene).
H. Eschway and W. Burchard, Polymer, Vol. 16, pp 180-184 (March, 1975), prepared a star polymer having 67 polystyrene arms and 67 polyisoprene arms by sequential anionic polymerization of sytrene, divinylbenzene and isoprene. Low concentrations of monomer were used to avoid gellation.
2. Preparation of Acrylic Star Polymers
In contrast to hydrocarbon star polymers (which may be prepared having different arm sizes, different numbers of arms and even with two different kinds of arms attached to the same core), acrylic star polymers have been available only in a limited variety of structures.
Although not making stars, L. R. Melby in U.S. Pat. No. 4,388,448 (June 14, 1983) does make glycidyl methacrylate polymers at low temperatures by anionic polymerization.
G. W. Andrews and W. H. Sharkey, U.S. Pat. No. 4,351,924 (1982), prepared acrylic star polymers having 3 or 4 hydroxyl-terminated arms by coupling acetal-ended, "living" poly(methyl methacrylate) with 1,3,5-tris(bromomethyl)benzene or 1,2,4,5-tetrabis(bromomethyl)benzene.
O. W. Webster, U.S. Pat. Nos. 4,417,034 (Nov. 22, 1983) and 4,508,880 (Apr. 2, 1985), and W. B. Farnham and D. Y. Sogah, U.S. Pat. Nos. 4,414,372 (Nov. 8, 1983) and 4,524,196 (June 18, 1985) showed that acrylic star polymers can be prepared via group transfer polymerization by coupling "living" polymer with a capping agent having more than one reactive site or by initiating polymerization with an initiator which can initiate more than one polymer chain. Initiators that could produce acrylic star polymers with up to 4 arms were demonstrated. See examples 5-7 of U.S. Pat. No. 4,508,880.
I. B. Dicker, et al., U.S. Pat. No. 4,588,795 (May 13, 1986) claims a preferred method of group transfer polymerization using oxyanion catalysts. I. B. Dicker, et al., U.S. Pat. No. 4,622,372 (Nov. 11, 1986) claims an improved process with enhanced catalyst longevity. C. S. Hutchens and A. C. Shor, U.S. Ser. No. 782,257, filed Sept. 30, 1985, now U.S. Pat. No. 4,656,226, granted Apr. 7, 1987, claims acrylic pigment dispersant made by GTP, such as methyl methacrylate-glycidyl methacrylate AB dispersants with functional groups added.
H. J. Spinelli, in applications U.S. Ser. Nos. 771,682; 771,683; 771,684; 771,685; and 771,686, all filed Sept. 3, 1985, teaches the preparation of acrylic star polymers, optionally having functional groups in the cores and/or the arms, with more or less crosslinked cores. Preferably GTP techniques are used with arm-first, core-first, or arm-core-arm sequencing.
The above-cited Webster, Farnham, et. al., Dicker, et al., Hutchens, et al. and Spinelli patents and applications are incorporated herein by reference.
The following is an update of the status of the above-mentioned applications of Spinelli. Ser. Nos. 771,682 and 771,683 are now respectively U.S. Pat. Nos. 4,659,782, and 4,659,783, granted Apr. 21, 1987; Ser. No. 771,684 is now U.S. Pat. No. 4,695,607 granted Sept. 22, 1987; Ser. No. 771,685 was abandoned after refiling as divisional cases Ser. No. 914,714 and 914,715 on Sept. 30, 1986, now U.S. Pat. No. 4,794,144 and U.S. Pat. No. 4,810,756.
R. J. A. Eckert, U.S. Pat. No. 4,116,917 (1978), describing hydrocarbon star polymers suggested that small amounts of other monomers (e.g., methyl methacrylate) may be included (Col. 3, lines 22-28) and that ethylene dimethacrylate may be used as a coupling agent (Col. 5, lines 22-28). A similar suggestion is made by T. E. Kiovsky, U.S. Pat. No. 4,077,893, cited above.
J. G. Zilliox, P. Rempp and J. Parrod, J. Polymer Sci., Part C, Polymer Symposia No. 22, pp 145-156 (1968), describe the preparation, via anionic polymerization, of a mixture of star polymers having 3 to 26 polymethyl methacrylate arms attached to cores of ethylene glycol dimethacrylate. The mixture also contained linear polymethyl methacrylate. The article says the lengths of the individual branches were constant but that the number of branches per star "fluctuates considerably", giving rise to a very high polydispersity.
3. Uses of Star Polymers
Hydrocarbon star polymers have been used as additives to improve the impact strength of polyphenylene ether resins--W. R. Haaf et al., U.S. Pat. No. 4,373,055 (1983); dry nylon--W. P. Gergen et al. U.S. Pat. No. 4,242,470 (1980); rubber-modified polystyrene--A. Aoki et al, U.S. Pat. No. 4,304,881, cited above; and chlorinated polyvinyl chloride resins M. H. Lehr, U.S. Pat. No. 4,181,644 (1980).
Hydrocarbon star polymers have also been added to asphaltic concrete to improve the service life--C. R. Bresson, U.S. Pat. No. 4,217,259 (1980); to polyetherester resins to provide a desirable overall balance of properties--R. W. Seymoure, U.S. Pat. No. 4,011,286 (1977), and to lubricating oil to improve the viscosity index and act as a dispersant--T. E. Kiovsky, U.S. Pat. No. 4,077,893 (1978).
Hydrocarbon star polymers have also been used to prepare thermoplastics having good clarity by blending them with thermoplastic resins such as methyl methacrylate/styrene/butadiene copolymers, polyester urethanes, epoxides, acrylics, polycarbonates, polyesters, etc.,--E. L. Hillier, U.S. Pat. No. 4,048,254 (1977).